U.S. Pat. No. 6,396,587 is incorporated herein by reference and discloses an interferometer arrangement for recording depth profiles of an object using “white light interferometry”.
In white light interferometry, white light, that is light having a relatively short coherence length, is used. The coherence length of an optical signal is the length over which the signal is phase correlated. For a light source having a long coherence length as, for example, a helium-neon laser, the coherence length can be several kilometers, while for a broadband white light source as, for example the sun, the coherence length is only some micrometers. Light sources having such a short coherence length cause interference phenomena in a light beam path, which is split and then again superposed, only if the optical path length of the two light beam paths between splitting and superposition corresponds within a few optical path lengths, that is, if the optical path lengths correspond within the coherence length.
The interferometer arrangement disclosed in U.S. Pat. No. 6,396,587 includes a superluminescence diode for generating light, which can be used for white light interferometry. The light of this superluminescence diode is coupled into a measuring beam path and a reference beam path. The reference beam path includes a mirror as a reflector element. With the measuring beam path, an object is scanned for measuring its depth profile and/or the density of scattering light centers. The light reflected from the object and from the mirror is superposed on a sensor surface which includes a CCD-detector row. From the location of an interference pattern on the CCD-detector row, a difference in the optical path length of the light in the measuring beam path and the reference beam path can be determined. From the measured difference of the optical path lengths, the position of scattering centers for light in the scanned or depth-probed object is determined and graphically represented.
U.S. Pat. No. 5,321,501 is incorporated herein by reference and discloses an interferometer arrangement and a method for determining depth profiles of an object using short coherent light from a superluminescence diode. The short coherent light from the superluminescence diode is coupled into a measuring beam path and a reference beam path. With the light in the measuring beam path, a section of an object is scanned or depth probed. The light in the reference beam path is guided to a movable mirror which allows to adjust the optical path length in the reference beam path. The light of the measuring beam path and of the reference beam path are brought to interference on a photodetector. From the time variation of subsequent interference phenomena on the photodetector and the known position of the mirror in the reference beam path, the position of scattering centers in the measuring branch is determined.